In a multimedia age, optical recording media such as CD-R (a write-once memory using compact disc) and DVD-R (a write-once memory using digital video disc) are now of great importance. Most of the conventional optical recording media can be roughly classified into inorganic optical recording media which have recording layers composed of inorganic substances such as tellurium, selenium, rhodium, carbon, or carbon sulfide; and organic optical recording media which have recording layers mainly composed of light absorbents containing organic dye compounds.
Among these optical recording media, organic optical recording media can be usually prepared by dissolving a polymethine dye in an organic solvent such as 2,2,3,3-tetrafluoro-1-propanol (abbreviated as “TFP” hereinafter), spin coating the solution onto the surface of a polycarbonate substrate, drying the solution to form a recording layer, and sequentially forming and coating onto the surface of the recording layer a reflection layer comprising a metal such as gold, silver or copper, and a protection layer comprising an ultraviolet ray hardening resin. When compared with inorganic optical recording media, organic ones may have the drawback that their recording layers are susceptible to change under environmental lights such as reading and natural light. Organic optical recording media, however, have the advantage that they can be made into optical recording media at a lesser cost because their recording layers can be directly formed by coating light absorbents in solution on the surface of substrates. Further, organic optical recording media composed of organic materials are now mainly used as low-cost optical recording media because they are substantially free of corrosion even when contacted by moisture or sea water and because information recorded therein in a prescribed format can be read out by using commercially available read-only readers after establishing thermal-deformation-type optical recording media, a kind of organic optical recording media.
What is urgently required in organic optical recording media is to increase their storage capacity to suit to this multimedia age. The research for such an increment, which is now being eagerly continued in this field, is to increase the recording capacity per one side from 4.7 GB (giga bite) to 15 GB or more by shortening the wavelength for writing information to 450 nm or less from the wavelengths of 635-650 nm which are commonly used. The high-density optical recording media have the capacity to record movie and animations for six hours in picture quality of standard television or for two hours even in relatively-high picture quality of high definition television. However, since most organic dye compounds now used in the conventional optical recording media cannot be used with visible light with a wavelength of 450 nm or less, they could not fulfil the need for high-storage density required in many fields.
In view of the foregoing, the object of the present invention is to provide organic dye compounds which have absorption maxima at a wavelength of 400 nm or less and substantially absorb a visible light with a wavelength of 450 nm or less when formed in a thin layer, and to provide uses thereof.